Recently, the use of a flexible metal clad laminate for a flexible printed circuit board is gradually increasing due to miniaturization and multi-functionalization of devices using the flexible printed circuit boards. The flexible metal clad laminate is formed of two layers including a metal layer such as a copper foil or an aluminum foil and a polymer film layer.
The polymer film applied to the metal clad laminate for the flexible printed circuit board needs to satisfy the following main properties to be suitable for the performance of a semiconductor and the conditions of a semiconductor packaging manufacturing process.
(1) A low thermal expansion coefficient that may correspond to a metal thermal expansion coefficient
(2) A low dielectric constant and dielectric stability in a high frequency region of 1 GHz or greater
(3) Heat resistance to a reflow process at a temperature of about 260° C.
(4) Low hygroscopicity to improve reliability
A polyimide resin having high heat resistance is used in a casting manner to prepare a conventional metal foil coated with a resin. Also, a polyamic acid solution is coated on the metal foil and then heat treated under appropriate conditions to be cured to manufacture a flexible metal clad laminate. The flexible metal clad laminate has a structure in which a polyimide resin layer is formed on the metal foil. Accordingly, the flexible metal clad laminate has excellent bending endurance and heat resistance, which are inherent properties of the polyimide resin, but has problems such as a warpage phenomenon caused by a difference in thermal expansion coefficients of the polyimide resin layer and the metal foil, and low dimensional stability due to high hygroscopicity of the polyimide resin itself.
Recently, the use of a wholly aromatic liquid polyester resin having high heat resistance or Teflon has been reviewed as an alternative measure to the use of the polyimide resin in the manufacturing process of the flexible metal clad laminate. However, to manufacture a wholly aromatic liquid crystalline polyester resin solution (i.e., varnish), a solvent containing a halogen element such as chlorine is needed, but in this case, problems such as corrosion of the metal foil due to the halogen element during the manufacturing processes of the flexible metal clad laminate and the flexible printed circuit board may occur and thus, the use of a non-halogen solvent is needed.